How important is cryptography?
Here's short answer for question on your thread title. Cryptography is necessary/very important for Bitcoin. Bitcoin (along with many modern software/infrastructure) can't be exist without it.
I am an enthusiast of bitcoin and am willing to know every bit of it because I believe is the future. Anything is acceptable so far it will aid my learning about bitcoin be it links, books, videos, pdf and pictures.
For cryptography specifically used by Bitcoin, you can
https://learnmeabitcoin.com/technical/ and scroll down to "Keys" section. Although resource mentioned by @albert0bsd is better option if you don't mind long read.